1. Field of the Invention
The present invention relates to a sheet post-processing apparatus performing post-processing on a folded portion of a bundle of sheets stacked and folded.
2. Description of Related Art
A conventional sheet post-processing apparatus performing post-processing on a sheet on which an image is formed performs saddle-stitch bookbinding, in which a sheet bundle acquired by collecting conveyed sheets is stitched in the vicinity of a center thereof in a conveyance direction for example, doubled at a stitched portion to make it in a booklet-like shape, and then discharged. In this case, the sheet post-processing apparatus thrusts the center portion of the sheet bundle with a thrust member after stitch processing is performed, and pushes the center portion thereof into a nip of a folding roller pair to fold the sheet bundle. Further, U.S. Pat. No. 7,802,779 discusses a sheet post-processing apparatus including a folding-line reinforcing mechanism for reinforcing a folding line of a booklet by moving a roller pair along the folding line while pressing the folding line. With such a configuration, quality, such as an appearance, of the bound sheet bundle can be enhanced.
The sheet post-processing apparatus discussed in the U.S. Pat. No. 7,802,779 may not be able to sufficiently reinforce the folding line only by pressing the folding line once with the roller pair, when the number of sheets forming the booklet is increased or the sheet having a large basis weight is used. Even in such a case, to realize sufficiently reinforcing the folding line, it is conceivable to intermittently move the roller pair, or to move them back and forth a plurality of times. However, such a method for moving the roller pair may take time to perform processing for reinforcing the folding line, thereby lowering productivity.